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Finish Lab: Stoichiometry and Gravimetric Analysis 2.Examining Data Calculate the mass of the dry precipitate (#6) by subtracting the mass of the filter paper (#3) and the mass of the beaker with paper towel (#4) from the total mass of beaker, paper towel, filter paper, and dried precipitate (#5). (#6 = #5 - #3 - #4) Record the mass of the dry precipitate in table. (#6) Use the molar mass of SrCO 3 to calculate the number of moles of precipitate formed.

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Finish Lab: Stoichiometry and Gravimetric Analysis 4.Evaluating Methods Calculate the #moles of SrCl 2 that were added if there was 0.30 mol SrCl 2 in every liter of solution. Was SrCl 2 or Na 2 CO 3 the limiting reactant? Na 2 CO 3 Would this experiment have worked if SrCl 2 was the limiting reactant? No, we wouldnt be able to determine how much Na 2 CO 3 was in the vat if we had excess Na 2 CO 3 left over after the reaction.

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Finish Lab: Stoichiometry and Gravimetric Analysis 5.Evaluating Methods Why was the SrCO 3 rinsed in step 11? To remove any impurities. What soluble impurities could have been on the filter paper along with the precipitate? NaCl How would the results vary if the precipitate had not been completely dry? The mass would have been greater due to the mass of the water.

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Finish Lab: Stoichiometry and Gravimetric Analysis 7.Applying Conclusions How many grams of Na 2 CO 3 are present in the 575 L drum? Hint: you just calculated how many grams of Na 2 CO 3 were in the 15 mL sample. Use that information as a conversion factor.

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Finish Lab: Stoichiometry and Gravimetric Analysis 8.Evaluating Methods We used a 0.5M solution, which means that there was 0.795 g Na 2 CO 3 for every 15 mL (this is the theoretical yield) Use your answer from question #6 as the actual yield and calculate the percentage yield: Actual yield X 100% Theoretical Yield

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Finish Lab: Stoichiometry and Gravimetric Analysis Dont forget your reflection statement: Was your hypothesis correct? How could you minimize the sources of errors that were mentioned in the lab in future trials? Did this lab help you to understand how stoichiometry could be used outside of the lab? Complete sentences!

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Finish Lab: Stoichiometry and Gravimetric Analysis Make sure your table of contents is updated and put your lab folders back in the bin to be graded.